A vehicle such as a truck, a bus, or a construction machine controls systems of a brake, a suspension, and the like using compressed air delivered by a compressor, which is directly connected to an internal combustion engine (hereinafter, an engine). The compressed air contains water from atmospheric air and lubricant oil from the interior of the compressor. If the compressed air containing water and oil enters the systems, rusting and swelling of rubber members (such as O rings) occur, thus hampering operation of the systems. Therefore, a compressed air drying device, which removes water and oil from compressed air, is arranged downstream of the compressor in an air system (see, for example, Patent Document 1).
The compressed air drying device has a filter and is filled with desiccant such as silica gel or zeolite. The desiccant of the compressed air drying device adsorbs and removes water from compressed air, thus drying the compressed air.
When performing load operation for removing water, the compressed air drying device causes compressed air, which is introduced through an inlet, to pass through a drying container from below to above. The compressed air drying apparatus retains the dry compressed air in a purge tank and, meanwhile, supplies the dry compressed air to a main tank through an outlet. When carrying out unload operation for regenerating the desiccant, the compressed air drying device opens a drain valve of a draining device to cause the dry compressed air retained in the purge tank to pass through the drying container from above to below, thus discharging oil and water through the drain valve. The compressed air drying device periodically performs the load operation and the unload operation in a repeated manner.